diff --git a/README.md b/README.md
index d801667..7632a0b 100644
--- a/README.md
+++ b/README.md
@@ -172,12 +172,13 @@ as `HERDR_PLUS_*` environment variables. If a command doesn't reference
 ## Worktree auto-layout
 
 herdr-plus can lay a project-style tab layout into a git **worktree** the moment
-herdr creates it. When you run `herdr worktree create` (or open one), herdr makes a
-fresh workspace for the worktree and fires a `worktree.created` event; herdr-plus
-catches it, finds a layout matching the worktree's repo, and opens that layout's
-tabs and panes in the new workspace — every command running — with no keypress.
-This is the plugin system's `[[events]]` hook (declared in
-[`herdr-plugin.toml`](herdr-plugin.toml)) put to work.
+herdr creates *or opens* it. When you run `herdr worktree create`/`open` (or use
+herdr's right-click worktree dialog), herdr makes a fresh workspace for the
+worktree and fires a `worktree.created` event (new worktree) or `worktree.opened`
+event (existing one); herdr-plus catches either, finds a layout matching the
+worktree's repo, and opens that layout's tabs and panes in the new workspace —
+every command running — with no keypress. This is the plugin system's `[[events]]`
+hook (declared in [`herdr-plugin.toml`](herdr-plugin.toml)) put to work.
 
 Layouts live in `~/.config/herdr-plus/worktrees/`, one TOML file per layout (the
 file name doesn't matter). A layout is a `repo` matcher plus the same `[[tabs]]`
diff --git a/herdr-plugin.toml b/herdr-plugin.toml
index 8169ea9..7f1680a 100644
--- a/herdr-plugin.toml
+++ b/herdr-plugin.toml
@@ -72,12 +72,20 @@ id = "ping"
 title = "Herdr Plus: ping"
 command = ["./bin/herdr-plus", "ping"]
 
-# worktree.created — fired by herdr every time it creates a git worktree. The
-# handler looks for a matching, enabled layout in ~/.config/herdr-plus/worktrees/
-# and lays its tabs/panes into the workspace herdr just made. It is a quiet no-op
-# when no layout matches (or the matching one has `enabled = false`), so it is
-# safe to subscribe unconditionally. herdr runs this for you — never invoke it by
-# hand. Output is captured in the plugin log.
+# worktree.created / worktree.opened — herdr fires worktree.created when it
+# creates a new git worktree and worktree.opened when it opens an existing one
+# into a workspace (e.g. the right-click dialog for a branch that already has a
+# worktree). Both hand us a fresh workspace that wants tabs, so we subscribe to
+# both — otherwise opening an existing worktree would silently skip the layout.
+# The handler looks for a matching layout in ~/.config/herdr-plus/worktrees/ and
+# lays its tabs/panes into the workspace. It is a quiet no-op when no layout
+# matches, and it skips a workspace that already has tabs (so a layout never
+# applies twice even if both events fire). herdr runs this for you — never invoke
+# it by hand. Output is captured in the plugin log.
 [[events]]
 on = "worktree.created"
-command = ["./bin/herdr-plus", "on-worktree-created"]
+command = ["./bin/herdr-plus", "on-worktree"]
+
+[[events]]
+on = "worktree.opened"
+command = ["./bin/herdr-plus", "on-worktree"]
diff --git a/herdr.go b/herdr.go
index 10364ec..39ce705 100644
--- a/herdr.go
+++ b/herdr.go
@@ -272,6 +272,30 @@ func (c *herdrClient) focusedPaneID() (string, error) {
 	return "", errors.New("no focused pane")
 }
 
+// workspacePaneCount returns how many panes currently live in the given
+// workspace. The worktree handler uses it as an idempotency guard: a freshly
+// created or opened worktree workspace has exactly one (root) pane, so a count
+// above one means the layout was already applied — and we should not apply it
+// again. On any socket error it returns 0 so the caller fails open (proceeds) and
+// degrades to the old, unguarded behavior rather than skipping wrongly.
+func (c *herdrClient) workspacePaneCount(workspaceID string) (int, error) {
+	var out struct {
+		Panes []struct {
+			WorkspaceID string `json:"workspace_id"`
+		} `json:"panes"`
+	}
+	if err := c.call("pane.list", map[string]any{}, &out); err != nil {
+		return 0, err
+	}
+	n := 0
+	for _, p := range out.Panes {
+		if p.WorkspaceID == workspaceID {
+			n++
+		}
+	}
+	return n, nil
+}
+
 // paneGet fetches metadata for a single pane, including its working directory
 // and the tab/workspace it belongs to.
 func (c *herdrClient) paneGet(paneID string) (paneInfo, error) {
diff --git a/main.go b/main.go
index 36c95b7..0f2a22b 100644
--- a/main.go
+++ b/main.go
@@ -23,8 +23,9 @@ import (
 //     pane it opens (the `picker` / `quick-actions-picker` entrypoints), so end
 //     users never run them directly.
 //   - "ping" is a smoke test that proves the plugin loop end to end.
-//   - "on-worktree-created" is herdr's worktree.created event handler — herdr runs
-//     it (via the [[events]] entry in herdr-plugin.toml), not the user.
+//   - "on-worktree" is herdr's worktree event handler, run for both worktree.created
+//     and worktree.opened (via the [[events]] entries in herdr-plugin.toml), not the
+//     user.
 //
 // The bare binary has no launcher of its own, so it just prints usage.
 func main() {
@@ -45,8 +46,8 @@ func main() {
 		case "ping":
 			runPing()
 			return
-		case "on-worktree-created":
-			runOnWorktreeCreated(os.Args[2:])
+		case "on-worktree":
+			runOnWorktreeEvent(os.Args[2:])
 			return
 		case "version", "--version", "-v", "-V":
 			fmt.Println("herdr-plus", version.Version)
diff --git a/worktree.go b/worktree.go
index 2013b0d..e9f99f1 100644
--- a/worktree.go
+++ b/worktree.go
@@ -18,11 +18,12 @@ import (
 )
 
 // WorktreeLayout is a declarative tab layout applied automatically when a herdr
-// git worktree is created. Where a Project is opened on demand and creates its
-// own workspace, a worktree layout reacts to herdr's `worktree.created` event:
-// herdr has already made the worktree's workspace, so the layout just fills it
-// with tabs. It reuses the same ProjectTab model, so worktree layouts get the
-// full single-command / split-pane vocabulary that projects have.
+// git worktree is created or opened. Where a Project is opened on demand and
+// creates its own workspace, a worktree layout reacts to herdr's worktree.created
+// and worktree.opened events: herdr has already made the worktree's workspace, so
+// the layout just fills it with tabs. It reuses the same ProjectTab model, so
+// worktree layouts get the full single-command / split-pane vocabulary that
+// projects have.
 //
 // Layouts live in ~/.config/herdr-plus/worktrees/, one TOML file per layout (the
 // file name does not matter). With no files there, the feature is simply inert.
@@ -172,7 +173,8 @@ type worktreeEvent struct {
 }
 
 // worktreeCreatedPayload mirrors the JSON herdr puts in HERDR_PLUGIN_EVENT_JSON
-// for a `worktree.created` event. Only the fields we use are declared.
+// for a worktree.created or worktree.opened event (the two share this shape).
+// Only the fields we use are declared.
 type worktreeCreatedPayload struct {
 	Data struct {
 		Workspace struct {
@@ -214,14 +216,16 @@ func parseWorktreeEvent(eventJSON string, getenv func(string) string) (worktreeE
 	}, nil
 }
 
-// runOnWorktreeCreated is the `worktree.created` event handler herdr invokes (via
-// the [[events]] entry in herdr-plugin.toml). It finds the enabled layout that
-// matches the new worktree and lays its tabs into the workspace herdr already
-// created. With no matching layout it does nothing — every worktree fires this, so
-// a quiet no-op is the common, correct case. Output goes to stdout/stderr, which
-// herdr captures in the plugin log (`herdr plugin log list --plugin
-// cloudmanic.herdr-plus`).
-func runOnWorktreeCreated(_ []string) {
+// runOnWorktreeEvent is the worktree event handler herdr invokes (via the
+// [[events]] entries in herdr-plugin.toml). herdr runs it for both
+// worktree.created (a new worktree) and worktree.opened (an existing worktree
+// reopened into a workspace); both hand us a fresh workspace that wants tabs, so
+// they share one handler. It finds the layout matching the worktree and lays its
+// tabs into the workspace herdr already created. With no matching layout it does
+// nothing — every worktree fires this, so a quiet no-op is the common, correct
+// case. Output goes to stdout/stderr, which herdr captures in the plugin log
+// (`herdr plugin log list --plugin cloudmanic.herdr-plus`).
+func runOnWorktreeEvent(_ []string) {
 	ev, err := parseWorktreeEvent(os.Getenv("HERDR_PLUGIN_EVENT_JSON"), os.Getenv)
 	if err != nil {
 		errExit("worktree event:", err)
@@ -242,8 +246,8 @@ func runOnWorktreeCreated(_ []string) {
 	}
 
 	// We need the workspace herdr made for the worktree and its root tab/pane to
-	// build on. They should always be present for a worktree.created event; bail
-	// loudly if not so the failure is visible in the plugin log.
+	// build on. They should always be present for a worktree event; bail loudly if
+	// not so the failure is visible in the plugin log.
 	if ev.WorkspaceID == "" || ev.RootTabID == "" || ev.RootPaneID == "" {
 		errExit(fmt.Sprintf("worktree event missing ids (workspace=%q tab=%q pane=%q)", ev.WorkspaceID, ev.RootTabID, ev.RootPaneID))
 	}
@@ -253,6 +257,18 @@ func runOnWorktreeCreated(_ []string) {
 		errExit(err)
 	}
 
+	// Idempotency guard. We subscribe to both worktree.created and worktree.opened,
+	// and herdr may also reopen a worktree workspace across sessions — so the
+	// handler can fire for a workspace we already laid out. A freshly created or
+	// opened worktree workspace has exactly one (root) pane, so more than one pane
+	// means the layout is already in place and we skip rather than stack a second
+	// copy of the tabs on top. A pane.list error returns 0, which fails open
+	// (proceeds) rather than wrongly skipping.
+	if n, err := client.workspacePaneCount(ev.WorkspaceID); err == nil && n > 1 {
+		fmt.Printf("herdr-plus: worktree workspace %q already has %d panes; skipping layout %q (already applied).\n", ev.WorkspaceID, n, layout.source)
+		return
+	}
+
 	if err := layoutTabs(client, ev.WorkspaceID, ev.RootTabID, ev.RootPaneID, layout.Tabs); err != nil {
 		errExit("apply worktree layout:", err)
 	}
diff --git a/www/content/docs/troubleshooting.md b/www/content/docs/troubleshooting.md
index 7a04486..be6ab33 100644
--- a/www/content/docs/troubleshooting.md
+++ b/www/content/docs/troubleshooting.md
@@ -76,9 +76,10 @@ the `working_dir` (remember `~` and `$VARS` expand). See [Projects](../projects/
 
 ## My worktree didn't get its layout
 
-Creating a git worktree opened a plain workspace instead of your tabs. The
-[worktree auto-layout](../worktrees/) handler runs on herdr's `worktree.created`
-event and logs why it did or didn't act — check the plugin log first:
+Creating or opening a git worktree gave you a plain workspace instead of your
+tabs. The [worktree auto-layout](../worktrees/) handler runs on herdr's
+`worktree.created` and `worktree.opened` events and logs why it did or didn't act
+— check the plugin log first:
 
 ```bash
 herdr plugin log list --plugin cloudmanic.herdr-plus
@@ -86,6 +87,11 @@ herdr plugin log list --plugin cloudmanic.herdr-plus
 
 Common causes:
 
+- **The worktree wasn't created through herdr.** herdr only fires these events for
+  worktrees it creates or opens itself (`herdr worktree create`/`open` or its
+  right-click worktree dialog). A worktree made with plain `git worktree add` — or
+  from lazygit or another tool — is invisible to herdr, so no event fires and no
+  layout applies. The plugin log will have **no** `on-worktree` entry at all.
 - **No file for that repo.** A layout is on only if a file for it exists in
   `worktrees/`. Confirm the file is there (not in `projects/`) and hasn't been
   deleted or moved.
diff --git a/www/content/docs/worktrees.md b/www/content/docs/worktrees.md
index 9474aab..975ecbf 100644
--- a/www/content/docs/worktrees.md
+++ b/www/content/docs/worktrees.md
@@ -1,24 +1,26 @@
 ---
 title: "Worktree Auto-Layout"
-description: "Automatically lay a project-style tab layout into a git worktree the moment herdr creates it, driven by the plugin's worktree.created event — with a per-layout on/off switch."
+description: "Automatically lay a project-style tab layout into a git worktree the moment herdr creates or opens it, driven by the plugin's worktree.created and worktree.opened events."
 weight: 65
 ---
 
 herdr-plus can open a project-style tab layout **automatically** when herdr
-creates a git worktree — no keypress, no picker. It's the plugin system's
-[`[[events]]`](https://herdr.dev/docs/plugins/) hook put to work: herdr-plus
-subscribes to the `worktree.created` event and fills the new worktree's workspace
-for you.
+creates or opens a git worktree — no keypress, no picker. It's the plugin
+system's [`[[events]]`](https://herdr.dev/docs/plugins/) hook put to work:
+herdr-plus subscribes to the `worktree.created` and `worktree.opened` events and
+fills the worktree's workspace for you.
 
 ## How it works
 
-When you run `herdr worktree create` (or `herdr worktree open`), herdr:
+When you run `herdr worktree create` (or `herdr worktree open`, or use herdr's
+right-click worktree dialog), herdr:
 
-1. Creates the git worktree.
+1. Creates or opens the git worktree.
 2. Makes a fresh herdr **workspace** for it, rooted at the worktree's directory.
-3. Fires a `worktree.created` event.
+3. Fires a `worktree.created` event (for a new worktree) or `worktree.opened`
+   event (for an existing one).
 
-herdr-plus catches that event, looks at the worktree's **repo** (and branch),
+herdr-plus catches either event, looks at the worktree's **repo** (and branch),
 finds a matching layout, and opens that layout's tabs and panes in the workspace
 herdr just made — running every startup command. Because herdr has already
 created the workspace and its first tab, herdr-plus only has to fill it in.
@@ -100,9 +102,9 @@ directory at all, it's simply inert.
 
 ## Where it runs
 
-The handler is the plugin's `worktree.created` event, declared in
-`herdr-plugin.toml`. herdr runs it for you (you never invoke it by hand), and its
-output is captured in the plugin log:
+The handler is wired to the plugin's `worktree.created` and `worktree.opened`
+events, declared in `herdr-plugin.toml`. herdr runs it for you (you never invoke
+it by hand), and its output is captured in the plugin log:
 
 ```bash
 herdr plugin log list --plugin cloudmanic.herdr-plus